Large enterprises and business organizations have their office or sales network spread all across the world. To provide network connectivity between these global sites a wide area network (WAN) is used. Simply worded, a WAN is a computer network that covers a wide area. This is in contrast with local area networks (LANs), which are restricted to a small and specific area. WANs are used to connect LANs to enable communication between computers in different locations. With the advent of internet, enterprises have stared using virtual private network (VPN) to interconnect their networks, forming a kind of WAN. Such enterprise customers obtain the VPN connectivity from service providers who provide MPLS/VPN services.
A virtual private network (VPN) can be defined as a network that uses a public telecom infrastructure to provide remote offices or individual users with secure access to their organization's network. Multi Protocol Label Switching (MPLS) VPN technology goes a step further. It provides a connection-oriented, cost efficient mechanism to manage applications between different locations. Enterprise customers with multiple sites are often connected by Layer 3 VPNs running over an MPLS WAN cloud. Typically, each of these sites has one or more CE (Customer Edge) routers connected to the MPLS cloud via the PE (Provider Edge) routers. The enterprise customers obtain these VPN services from service providers. These customers do not have management access to the PE routers and their management is limited only up to the CE routers.